lightbox not tracking with page responsive page

Im currently creating a site with a lightbox reg form on click,

I have placed the lightbox code in as an absolute position, but its obviously not tracking with the responsive page.

I therefore changed it to a relative position and the reg form ended up bumping down the page and would fit into the lightbox when activated.

Can someone please help as I'm at a loss...

a simple page can be found here without images ( http://ift.tt/1LDmjAr )

Lightbox and form .css below

}
#lightbox{
    display: none;
    float: left;
    position: absolute;
    top: 300px;
    left: 495px;
    width: 388px;
    height: 487px;
    background-color: #fff;
    margin-left: 820px;
    margin-top: 5px;
}
#formzone2 {
    width: 388px;
    height: 487px;
    float:left;
    margin-top:296px;
    margin-left:22px;}